|
(11) | EP 0 186 207 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
|
|
| (54) |
Thermal transfer recording apparatus Wärmeübertragungsaufzeichnungsgerät Appareil d'enregistrement à transfert thermique |
|
|
|||||||||||||||||||||||||||||||
| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
Background of the invention
[0001] The present invention relates to a thermal transfer recording apparatus which allows a thermal head to press on a platen roller, through ink and printing sheets interposed in between as set forth in the preamble of claim 1. Such apparatus is well known in the art and the principles thereof are generally shown in Fig. 1 of the drawings.
[0002] In an apparatus of this kind, thermal transfer recording is effected by causing an ink sheet, which is provided with an ink layer on one surface thereof, and a recording sheet into contact, then pressing a thermal head against the other surface of the ink sheet, and then applying a current to selected ones of heating resistors of the thermal head to heat the head. The heat of the head melts the ink on the ink sheet to transfer it to the recording sheet.
[0003] The known apparatus 10 for such thermal transfer recording, shown in Fig. 1, includes a platen roller 16, a thermal head 12, a support plate 14 adapted to support the thermal head 12 at one end thereof and pivotally movable about a fulcrum A to bring the head 12 into and out of the vicinity of the platen roller 16, and a pull-type solenoid device 18 having a plunger or drive shaft 18a, which is connected to the other end of the support plate 14 and directly reciprocated to move the support plate 14 in the above-mentioned manner. The head 12 is brought into the vicinity of the platen roller 16 by the pull-type solenoid device 18 (see arrow a) and driven away from the platen roller 16 by a spring 20, as shown by arrow b.
[0004] As described above, movements of the head into and out of pressing contact with the platen roller with the sheets interposed in between have customarily been implemented with the pull-type solenoid mounted on one end of the head support plate, which is movable in a seesaw motion, and the spring. The problem with this prior art apparatus is that when the solenoid device is actuated to press the head against the platen roller, the spring counteracts the solenoid device, as is shown in Fig. 1 by arrows c and d. Specifically, the head fails to press on the platen roller with sufficient force F (which should generally be about 100 N) unles the support plate is dimensioned longer between the fulcrum and the head than between the fulcrum and the drive shaft of the solenoid device or a large-scale pull-type solenoid device is used. This makes the whole apparatus bulky and aggravates power consumption.
[0005] Another problem with the prior art apparatus is that since the release of the head from the platen roller is effected by the spring which is anchored to the support plate, a substantial period of time is necessary for the head from being moved clear of the platen roller after the solenoid device is deenergized, that is, rapid release of the head is unattainable. In addition, such a slow escapement of the head away from the platen roller increases a chance of head collision with the platen roller at its protruding paper cramp.
Summary of the invention
[0006] It is therefore an object of the present invention to provide a thermal transfer recording apparatus as set forth above which allows a thermal head to press forward a platen roller with an optimum force, rapidly.
[0007] This object is attained by the characterizing features of claim 1. A preferred embodiment of the invention is subject-matter of the dependent claim.
[0008] The above object, the features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings.
Brief description of the drawings
[0009]
Fig. 1 is a fragmentary sectional side elevation of a prior art thermal transfer recording apparatus;
Fig. 2 is a fragmentary side elevation of a thermal transfer recording apparatus embodying the present invention;
Fig. 3 is a perspective view of the recording apparatus of Fig. 2;
Fig. 4 is an enlarged view of a flat member which is included in the recording apparatus of Figs. 2 and 3 and provided with a slot; and
Fig. 5 is a diagram representative of the operation of a second cam also included in the recording apparatus of Figs. 2 and 3.
Description of the preferred embodiment
[0010] Referring to Figs. 2 and 3, a thermal transfer recording apparatus embodying the present invention which is free from the above-discussed drawbacks is shown. The apparatus, generally 30, includes a thermal head 32 which is mounted on a support plate 34. As shown in Fig. 3, the support plate 34 has a first portion 34a and a second portion 34b which is narrower than the first portion 34a. The support plate 34 is movable in a seesaw motion about a fulcrum B. A platen roller 36 is made of an elastic material such as rubber and located below the thermal head 32. A rotary solenoid 38 which accommodates a spring therein has a rotary plunger 38a to which a rotary shaft 40 is connected. The rotary-type solenoid device is smaller in size than the pull-type solenoid device used with the prior art apparatus and, yet produces a considerable torque which insures sufficient pressure of the head 32 with the platen roller 36. A first cam 42 is mounted on the rotary shaft 40, while a pin 34c extends downwardly from the other end of the support plate 34. The upper surface of the free end of the first cam 42 faces the lower end of the pin 34c. Alternatively, the pin 34c may be provided on the first cam 42 which is fixed to the rotary shaft 40, or a roller may be provided on the free end of the pin 34c which is not fixed in place. A pair of spaced second cams 44 are also mounted on the rotary shaft 40. Pins 44a are each studded in the free end of the second cam 44 and movably received in a slot 46a which is formed through flat member 46. A separator roller 52 is supported by one end of the flat members 46 in order to separate an ink sheet 50 which is dispensed from an ink sheet roller 48. The reference numeral 54 designates an ink sheet take-up roller, and 56 a recording sheet. A symbol C designates the center of rotation of the flat members 46. The slots 46a of the flat members 46 allow one to freely move the support plate 34 or the flat member 46 to thereby raise the thermal head 32 away from the platen 36 or release the roller 52 from the ink sheet 50 in the event of, for example, replacement of the ink sheet 50. As shown in Fig. 4, the slots 46a each merge into a slightly enlarged portion 46b at the upper end which is complementary in configuration to the pin 44a.
[0011] As shown in Fig. 5, assume a circle having a radius which is defined by a line interconnecting the center of the pin 44a on any of the second cams 44 and the center of rotation C of the flat members 46, and with center at the center of rotation C. In this particular embodiment, a line tangential to such a circle at the position of the pin 44a is located above the center of the rotary shaft 38a.
[0012] In operation, the first cam 42 which is rotated by the rotary solenoid device 48 raises the adjacent end of the support plate 34 and, thereby, causes the thermal head 32 into pressing toward with the platen roller 36. In such a construction, even if the support plate 34 has the same dimensions as that of the prior art apparatus in both of its extensions at opposite sides of the center of rotation B of its own, the thermal head 32 is capable of pressing toward the platen roller 36 with a stronger force than in the prior art apparatus. In the illustrative embodiment, the second cams 44 which are also mounted on the rotary shaft 40 serve as another source of pressure force which urges the head 32 against the platen roller 56 as explained infra. Specifically, while the first cam 42 is rotated to hold the head 32 in pressing against the platen roller 36, the second cams 44 are also rotated to cause the head 32 to further strongly press against the platen roller 36.
[0013] In detail, a force F, is imparted by the tension of the ink sheet 50 upwardly to the separator roller 52 which is separating the ink sheet 50. In this condition, as shown in Fig. 5, a torque x,Fcos 8 is developed about the center of rotation C of the flat member 46 with the result that a force F2=Xl/ X2. Ficos 8 acts on the second cams 44. At this instant, the vector of the force F2 which acts on the pins 44a on the second cams 44 assumes a position on a circle having a radius which is defined by a line interconnecting the centers of the pins 44a and the center of rotation C of the flat members 46 and with center at the center of rotation C, and above the center of the rotatable plunger 38a. Therefore, the force acting on the pins 44a acts on the rotary shaft 40, which is associated with the solenoid device 38, with a torque F2. x3 and in the clockwise direction as viewed in Fig. 2.
[0014] In the above situation, the torque acting on the shaft 40 also acts on the first cam 42 so that the force F which the first cam 42 exerts on the head 32 toward the platen roller 36 is intensified. In the case where the diameter of the ink sheet rolled on the take-up roller 54 is relatively small or where the tension of the ink sheet 50 is relatively weak, the force F, and, therefore, the torque developing about the center of rotation C of the flat members 46 will correspondingly be reduced to in turn reduce the pressing force of the head 32 against the platen roller 36.
[0015] To release the head 32 from the platen roller 36, a power supply associated with the solenoid device 38 is turned off. Then, the spring which is installed in the solenoid device 38 restores the first cam 42 to its original or inoperative position via the plunger 38a and shaft 40. This causes that part of the support plate 34 which is connected with the first cam 42 to be pulled downwardly and, thereby, the other part which carries the head 32 therewith upwardly from the fulcrum B. In this manner, the thermal head 32 is rapidly moved clear of the platen roller 36.
[0016] In summary, it will be seen that the present invention provides a thermal transfer recording apparatus which with an extremely simple construction allows a thermal head to be pressed strongly against a platen roller. The simplicity of construction translates into a low production cost. The whole apparatus is small size and light weight and consumes a minimum of power. In addition, when a power supply is turned off, the head is immediately released from whe platen roller to enhance stability and reliability of operation.
a head support plate (34) carrying the thermal head (32) at one end portion (34a)
thereof and pivotally movable in a seesaw motion about a fulcrum (B), which is located
between said one end portion (34a) and another end portion (34b) of said head support
plate (34), and a solenoid (38) operatively engaging said other end portion (34b)
of said head support plate (34) and generating a drive force which causes said support
plate (34) to move about the fulcrum (B),
characterized in that said solenoid is a rotary solenoid (38) and that a pressing
device (40, 42, 34c; 44, 46, 52) is connected to said rotary solenoid (38) for pressing
the thermal head (32) against the platen roller (36) by transmitting the drive force
generated by said rotary solenoid (38) to the head support plate (34), said pressing
device comprising:
first pressing means comprising a rotary shaft (40) connected to a rotary plunger (38a) of the rotary solenoid device (38) and a first cam (42) rigidly mounted on said rotary shaft (40) and a pin (34c) studded in the other end portion (34b) of the head support plate (34) to be engaged by said first cam (42), and
second pressing means subjected to a tension of the ink sheet (50) during recording for intensifying pressing force of the head (32) againsl the platen (36) by transmitting an extra drive force resulting from the tension of the ink sheet (50) via the first pressing means (40, 42, 34c) to the head support plate (34), said second pressing means comprising a pair of second cams (44) rigidly mounted on the rotary shaft (40), a pair of elongate flat members (46), each one being operatively linked with a respective one of said second cams (44) and pivotally movable about a fulcrum (C), and an ink sheet separator roller (52) rotatably supported by one end of the flat members (46), each one of said flat members (46) being formed with an elongate slot (46a) through the other end portion thereof, in which a pin affixed to an associated one of the second cams (44) is movable received.
eine Kopftragplatte (34), die den Thermokopf (32) an einem Endabschnitt (34a) derselben
trägt und schwenkbar in einer Kippbewegung um ein Schwenklager (B) beweglich ist,
das zwischen dem genannten einen Endabschnitt (34a) und einem weiteren Endabschnitt
(34b) der Kopftragplatte (34) gelegen ist, und einen Elektromagneten (38), der wirkungsmäßig
den genannten anderen Endabschnitt (34b) der Kopftragplatte (34) ergreift und eine
Antriebskraft erzeugt, die die Tragplatte (34) veranlaßt, sich um das Schwenklager
(B) zu bewegen;
dadurch gekennzeichnet, daß der Elektromagnet ein Elektrodrehmagnet (38) ist, und
daß eine Druckeinrichtung (40, 42, 34c; 44, 46, 52) mit dem Elektrodrehmagnet (38)
verbunden ist, um den Thermokopf (32) gegen die Walze (36) zu drücken, indem die von
dem Elektrodrehmagnet (38) erzeugte Antriebskraft auf die Kopftragplatte (34) übertragen
wird, welche Druckeinrichtung enthält:
eine erste Druckeinrichtung, enthaltend eine Drehwelle (40), die mit einem Drehanker (38a) des Elektrodrehmagneten (38) und einem ersten Nokken (42) verbunden ist, der fest an der Drehwelle (40) angebracht ist, und einen Stift (34c), der in den anderen Endabschnitt (34b) der Kopftragplatte (34) eingesetzt ist, um von dem ersten Nocken (42) erfaßt zu werden, und
eine zweite Druckeinrichtung, die einer Spannung des Farbblatts (50) während der Aufzeichnung unterworfen ist, um die Druckkraft des Kopfes (32) gegen die Walze (36) zu intensivieren, indem eine Extraantriebskraft, die aus der Spannung des Farbblattes (50) resultiert, über die erste Druckeinrichtung (40, 42, 34c) auf die Kopftragplatte (34) übertragen wird, welche zweite Druckeinrichtung ein Paar zweiter Nocken (44) enthält, die starr an der Drehwelle (40) befestigt sind, sowie zwei langgestreckte flache Elemente (46), die jeweils wirkungsmäßig mit einem der zweiten Nocken (44) verbunden und um eine Drehachse (C) schwenkbar beweglich sind, und eine Tintenblatttrennwalze (52), die drehbar durch eine Ende der flachen Elemente (46) gehalten ist, wobei jedes der flachen Elemente (46) mit einem langgestreckten Schlitz (46a) durch den anderen Endabschnitt desselben versehen ist, in welchem ein Stift, der an einem zugeordneten der zweiten Nocken (44) befestigt ist, beweglich aufgenommen ist.
une plaque support de tête (34) portant la tête thermique (32) à sa première portion
d'extrémité (34a) et pouvant pivoter, selon un mouvement de bascule, autour d'un pivot
(B), situé entre ladite première portion d'extrémité (34a) et une autre portion d'extrémité
(34b) de ladite plaque support de tête (34), ainsi qu'un électro-aimant (38) venant
opérationnellement en prise avec ladite autre portion d'extrémité (34b) de ladite
plaque support de tête.(34) et produisant une force d'entraînement qui oblige ladite
plaque support (34) à se mouvoir autour du pivot (B);
caractérisé en ce que ledit électro-aimant est un électro-aimant tournant (38); et
en ce qu'un dispositif de pressage (40, 42, 34c; 44, 46, 52), est relié audit électro-aimant
tournant (38) pour presser la tête thermique (32) contre le rouleau d'impression (36)
en transmettant la force d'entraînement, produite par ledit électro-aimant tournant
(38), à la plaque support de tête (34), ledit élément de pressage comportant:
un premier moyen de pressage comprenant un arbre tournant (40) relié à un plongeur tournant (38a) du dispositif (38) formant électro-aimant tournant et une première came (42) rigidement montée sur ledit arbre tournant (40) et une broche (34c) boulonnée dans l'autre portion d'extrémité (34b) de la plaque support de tête (34) pour que ladite première came (42) vienne en prise avec elle,
un second moyen de pressage, soumis à une tension de la feuille encreuse (50) au cours de l'enregistrement, pour intensifier la force de pressage de la tête (32) contre le rouleau d'impressin (36) en transmettant une force d'entraînement supplémentaire, résultant de la tension de la feuille encreuse (50), par l'intermédiaire du premier moyen de pressage (40, 42, 34c), à la plaque support de tête (34), ledit second moyen de pressage comprenant une paire de secondes cames (44) rigidement montées sur l'arbre tournant (40), une paire d'organes plats (46) de forme allongée, dont chacun est relié opérationnellement avec l'une, respective, desdites secondes cames (44) et peut pivoter autour d'un pivot (C), ainsi qu'un rouleau (52), séparateur de la feuille encreuse et supporté en rotation par l'une des extrémités des organes plats (46), chacun desdits organes plats (46) étant formé avec, à travers sont autre portion d'extrémité, une fente de forme allongée (46a) dans laquelle peut se déplacer une broche fixée à l'une, associée, des secondes cames (44).